Object detection apparatus

ABSTRACT

An object detection apparatus includes a first acquisition unit that acquires, as a first direct wave group, reflected versions of first probing waves transmitted from and received at a first position, and acquires, as a first indirect wave group reflected versions of the first probing waves received at a second position, a second acquisition unit that acquires, as a second indirect wave group, reflected versions of second probing waves transmitted from the second position and received at the first position, and acquires, as a second direct wave group, reflected versions of the second probing wave received at the second position, and a determination unit that determines whether the object is a real object or a ghost in accordance with the receptions times of the first and second direct wave groups and the first and second indirect wave groups.

This application claims priority to Japanese Patent Application No.2014-215093 filed on Oct. 22, 2014, the entire contents of which arehereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an object detection apparatus.

2. Description of Related Art

It is known to equip a vehicle with distance sensors such as ultrasonicsensors to detect an object present in the vicinity of the vehicle, suchas a preceding vehicle, a pedestrian, or an obstacle to enableperforming various control operations such as starting of a brakeapparatus, or notification to a vehicle driver in accordance withresults of the object detection for the purpose of increasing runningsafety of the vehicle.

When an object is present outside a vehicle width area of the vehicle,the risk of a collision between the vehicle and the object is small.However, if only the distance between the vehicle and the object ismeasured without detecting the position of the object in the vehiclewidth direction perpendicular to the running direction of the vehicle,it may be determined that there is a risk of a collision with the objectand the vehicle driver is informed to that effect, although the objectis present outside the vehicle width area.

Japanese Patent Application Laid-open No. 2014-89077 describes an objectdetection apparatus for detecting a position in the vehicle widthdirection of an object which is ahead of a vehicle on which the objectdetection apparatus is mounted. This object detection apparatus includestwo distance sensors mounted on a vehicle, and calculates the positionof an object in the vehicle width direction using a triangulationmethod. This object detection apparatus determines that there is a riskof a collision with the object when the calculated position is within avehicle width area of the vehicle, and determines that there is no riskof collision with the object when the calculated position is outside thevehicle width area. This object detection apparatus is capable ofpreventing a brake apparatus from being operated when there is no objectwithin the vehicle width area.

However, the object detection apparatus described in the above patentdocument has the following problem. This object detection apparatus candetect only one object per one object-detection cycle. Morespecifically, when a plurality of objects are present ahead of thevehicle, the object detection apparatus detects only one of the objectswhich is the closest to the vehicle, but cannot detect the otherobjects. Accordingly, in a situation where the closest object is outsidethe vehicle width area, but another object which is more distant fromthe vehicle than the closest object is exists within the vehicle widtharea, there is a concern that the brake apparatus does not operatealthough there is a risk of a collision.

SUMMARY

An exemplary embodiment provides an object detection apparatus fordetecting at least one object present in a vicinity thereof bytransmitting first probing waves from a first position and subsequentlytransmitting second probing waves from a second position different fromthe first position, a detection area of the first probing waves and adetection area of the second probing waves being partially overlappedwith each other, and by receiving reflected versions of the first andsecond probing waves as detection data of the object, including:

a first acquisition unit that acquires, as a first direct wave groupincluding first direct waves, the reflected versions of the firstprobing waves received as the first direct waves at the first position,and acquires, as a first indirect wave group including first indirectwaves, the reflected versions of the first probing waves received as thefirst indirect waves at the second position;

a second acquisition unit that acquires, as a second indirect wave groupincluding second indirect waves, the reflected versions of the secondprobing waves received as the second indirect waves at the firstposition, and acquires, as a second direct wave group including seconddirect waves, the reflected versions of the second probing wavesreceived as the second direct waves at the second position;

a first calculation unit that calculates a position of the object inaccordance with combinations each including one of the first directwaves and one of the first indirect waves;

a second calculation unit that calculates the position of the object inaccordance with combinations each including one of the second directwaves and one of the second indirect weaves; and

a determination unit that determines whether the object is a ghost ornot depending on whether the position of the object has been calculatedby both the first and second calculation units or has been calculated byonly one of the first and second calculation units; wherein

the determination unit determines that the object whose position iscalculated by the first calculation unit is a real object if adifference of a distance to the object detected based on reception timesof the first direct waves and a distance to the object detected based onreception times of the first indirect waves is larger than apredetermined threshold, and determines that the object whose positionis calculated by the second calculation unit is a real object if adifference of a distance to the object detected based on reception timesof the second direct waves and a distance to the object detected basedon reception times of the second indirect waves is larger than apredetermined threshold.

According to the exemplary embodiment, there is provided an objectdetection apparatus capable of correctly detecting a plurality ofobjects present in the vicinity of the object detection apparatus.

Other advantages and features of the invention will become apparent fromthe following description including the drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a diagram schematically showing the structure of an objectdetection apparatus according to an embodiment of the invention;

FIG. 2 is a diagram for explaining a method of calculating the positionof an object;

FIG. 3 is a diagram for explaining a method of calculating the positionsof two objects;

FIG. 4 is a diagram showing an example in which the position of a ghostis calculated;

FIG. 5 is a diagram showing a situation in which direct waves andindirect waves are received by a direct wave detection sensor and anindirect wave detection sensor which have been switched with each other;

FIG. 6 is a diagram showing a situation in which direct waves andindirect waves are received by the direct wave detection sensor and theindirect wave detection sensor when a second object is present in thedistance;

FIG. 7 is a diagram showing a situation in which the direct waves andthe indirect waves are received by the direct wave detection sensor andthe indirect wave detection sensor which have been switched with eachother contrary to the situation shown in FIG. 6; and

FIG. 8 is a flowchart showing steps of an object detection processperformed by the object detection apparatus according to the embodimentof the invention.

PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 is a diagram schematically showing the structure of an objectdetection apparatus according to an embodiment of the invention.

In FIG. 1, the reference numeral 20 denotes a distance sensor (anultrasonic sensor in this embodiment). The distance sensor 20 has afunction of transmitting ultrasonic waves of 20 kHz to 200 kHz asprobing waves, and a function of receiving the probing waves reflectedfrom an object as returning waves. In this embodiment, four distancesensors (collectively designated by the reference numeral 20) aremounted to a front part (the front bumper, for example) of a vehicle 30such that they are arranged with a distance in the vehicle widthdirection perpendicular to the running direction of the vehicle 30. Morespecifically, the distance sensors 20 includes first and second sensors21 and 22 disposed near the center line of the vehicle 30 symmetricallywith respect to the center line 31 of the vehicle 30, and third andfourth sensors 23 and 24 disposed at the left and right corners of thevehicle 30, respectively. Although not explained here, the distancesensors 20 are mounted also to a rear part (the rear bumper, forexample) of the vehicle 30 in a similar way as those mounted to thefront part of the vehicle 30.

Each of the distance sensors 20 is assigned to an object detection area(collectively designated by the reference numeral 40) in which it canreceive the returning waves (or direct waves) of the probing waves whichit transmits. The distance sensors 20 are mounted such that two objectdetection areas 40 of each adjacent two of the distance sensors 20partially overlap with each other. In FIG. 1, only the object detectionareas 41 and 42 are shown, however, actually, the object detection area40 is set for each of the third and fourth sensors 23 and 24. Anamplitude threshold is set for each distance sensor 20. When thedistance sensor 20 has received the returning waves having an amplitudelarger than this threshold, the distance sensor 20 sends detection dataincluding the time at which the returning waves were received to an ECU10 as an object detection apparatus.

The ECU 10, which is a microcomputer-based unit including a CPU andmemory devices, determines presence or absence of an object 50 in thevicinity of the vehicle 30 based on the detection data sent from thedistance sensors 20. The ECU 10 commands each distance sensor 20 totransmit the probing waves every transmission cycle with a predeterminedtime interval (several hundred milliseconds, for example) by sending acontrol signal to each distance sensor 20.

When the ECU 10 determines that the object 50 is present in the vicinityof the vehicle 30, the ECU 10 performs steering control or brakingcontrol as collision preventing control, or informs the vehicle driverof the vehicle 30 by a warning sound.

The ECU 10 calculates the position of the object 50 relative to thevehicle 30 using a triangulation method based on the detection datareceived from the distance sensors 20. The triangulation method is suchthat the coordinates of a measurement point is calculated based on thedistance between known two points and distances to the known two points.The ECU 10 calculates the position (coordinates) of the object 50 basedon the distance of the two adjacent distance sensors 20 whose detectionareas 40 partially overlap with each other, and the distances betweenthe object 50 and theses distance sensors 20.

An example of the method of calculating the position of the object 50 isexplained in more detail with reference to FIG. 2. In this example, thefirst sensor 21 is used as a direct detection sensor which transmitsprobing waves 25 and receives returning waves of the probing waves 25 asdirect waves 26 at a first position, and the second sensor 22 is used asan indirect wave detection sensor which receives the returning waves ofthe probing waves 25 transmitted from the first sensor 21 as indirectwaves 27 at a second position.

The ECU 10 calculates, as an estimated position of the object 50, anx-coordinate and a y-coordinate of the position of the object 50 in ancoordinate system whose X-axis passes through the first and secondsensors 21 and 22, and whose Y-axis passes through the middle pointbetween the first and second sensors 21 and 22 and is perpendicular tothe X-axis. The ECU 10 causes the first sensor 21 to transmit theprobing waves 25. When a reflected version of the probing waves 25 arereceived as the direct waves 26 by the first sensor 21, the ECU 10calculates the distance between the first sensor 21 and the object 50 inaccordance with the direct waves 26. Further, when the reflected versionof the probing waves 25 is received as the indirect waves 27 by thesecond sensor 22, the ECU 10 calculates the distance between the secondsensor 22 and the object 50 in accordance with the indirect waves 27.

The distance d between the first sensor 21 and the origin point O of thecoordinate system, or the intersection point of the X-axis and theY-axis, which is the same as the distance between the second sensor 22and the origin point O, is stored beforehand in the ECU 10. Also, theECU 10 calculates, as a first time period t1, the time at which thedirect waves 26 were received by the first sensor 21 minus the time atwhich the probing waves 25 were transmitted by the first sensor 21, andcalculates, as a second time period t2, the time at which the indirectwaves 27 were received by the second sensor 22 minus the time at whichthe probing waves 25 were transmitted by the first sensor 21. Theproduct of the first time period t1 and the speed of the sound is equalto twice the distance between the first sensor 21 and the object 50, andthe product of the second time period t2 and the speed of the sound isequal to the sum of the distance between the first sensor 21 and theobject 560 and the distance between the second sensor 22 and the object50. The ECU 10 calculates the coordinates (x, y) of the object 50 byperforming the triangulation method using the distance 2 d between thefirst and second sensors 21 and 22, the first time period t1, and thesecond time period t2.

In the example of FIG. 2, the first sensor 21 is used as a directdetection sensor and the second sensor 22 is used as an indirectdetection sensor. However, it is possible to calculate the position ofthe object 50 in a similar manner also when the first sensor 21 is usedas an indirect detection sensor and the second sensor 22 is used as adirect detection sensor. In this embodiment, the position of the object50 is calculated for each combination of adjacent two of the distancesensors 21 to 24 mounted to the front part of the vehicle 30. Likewise,the position of the object 50 is calculated for each combination ofadjacent two distance sensors 20 mounted to the rear part of the vehicle30.

Incidentally, there are cases where two objects are present within theobject detection area 40. FIG. 3 shows an example of such cases, inwhich a first object 50 a and a second object 50 b are present withinthe object detection area. Here, it is assumed that the distance betweenthe first sensor 21 and the first object 50 a is equal to a firstdistance L1, the distance between the first sensor 21 and the secondobject 50 b is equal to a second distance L2, the distance between thesecond sensor 22 and the first object 50 a is equal to a third distanceL3, and the distance between the second sensor 22 and the second object50 b is equal to a fourth distance L4. Also, it is assumed that thesecond distance L2 is larger than the first distance L1.

The probing waves 25 transmitted from the first sensor 21 are reflectedby the first object 50 a and the second object 50 b, and enter the firstsensor 21 as first direct waves 26 and second direct waves 28,respectively. Also, the probing waves 25 are reflected by the firstobject 50 a and the second object 50 b, and enter the second sensor 22as first indirect waves 27 and second indirect waves 29, respectively.

At this time, the propagation time of the first direct waves 26 dependson the first distance L1, and the propagation time of the second directwaves 28 depends on the second distance L2. Accordingly, there is a timedifference between the incident time of the first direct waves 26 (thetime at which the first direct waves 26 enter the first sensor 21) andthe incident time of the second direct waves 28 (the time at which thesecond direct waves 28 enter the first sensor 21), the time differencedepending on the difference between the first distance L1 and the seconddistance L2. Likewise, the propagation time of the first indirect waves27 depends on the third distance L3, and the propagation time of thesecond indirect waves 29 depends on the fourth distance L4. Accordingly,there is a time difference also between the incident time of the firstindirect waves 27 and the incident time of the second indirect waves 29depending on the difference between the sum of the first distance L1 andthe third distance L3 and the sum of the second distance L2 and thefourth distance L4.

To calculate the positions of the objects 50 a and 50 b by thetriangulation method, one of the first direct waves 26 and the seconddirect waves 28 and one of the first indirect waves 27 and the secondindirect waves 29 are used.

The positions of the objects 50 a and 50 b can be correctly calculatedby performing the triangulation method using the combination of thefirst direct waves 26 and the first indirect waves 27 and thecombination of the second direct waves 28 and the second indirect waves29. However, although there is a difference between the incident time ofthe first indirect waves 27 reflected from the first object 50 a and theincident time of the second indirect waves 29 reflected from the secondobject 50 b, it is not possible to determine from which of the objects50 a and 50 b they are reflected based on only these incident times.

Accordingly, it is necessary to decide whether the triangulation methodshould be performed based on the combination of the first direct waves26 and the first indirect waves 27 and the combination of the seconddirect waves 28 and the second indirect waves 29, or based on thecombination of the first direct waves 26 and the second indirect waves29 and the combination of the second direct waves 28 and the firstindirect waves 27.

This is because if the triangulation method is performed based on thecombination of the first direct waves 26 and the second indirect waves29 and the combination of the second direct waves 28 and the firstindirect waves 27, a position of a ghost is calculated.

FIG. 4 shows an example in which the position of a first ghost 51 a iscalculated using the first direct waves 26 and the second indirect waves29, and the position of a second ghost 51 b is calculated using thesecond direct waves 58 and the first indirect waves 27. The position ofthe first ghost 51 a is calculated as a position distant from the firstsensor 21 by the first distance L1, and distant from the second sensor22 by the sum of the second distance L2 and the fourth distance L4 minusthe first distance L1. The position of the second ghost 51 b iscalculated as a position distant from the second sensor 22 by the seconddistance L2, and distant from the first sensor 21 by the sum of thefirst distance L1 and the third distance L3 minus the second distanceL2.

To determine whether the calculated position is the position of a realobject or the position of a ghost, the direct detection sensor and theindirect detection sensor are switched with each other. Specifically, asshown in FIG. 5, the second sensor 22 is used as a direct detectionsensor, and the first sensor 21 is used as an indirect detection sensor.

Probing waves 25 a transmitted from the second sensor 22 are reflectedby the second object 50 b and the first object 50 a, and enter thesecond sensor 22 respectively as first direct waves 26 a and seconddirect waves 28 a. Also, the probing waves 25 a are reflected by thefirst object 50 a and the second object 50 b, and enter the first sensor21 respectively as first indirect waves 27 a and second indirect waves29 a.

The positions of the second object 50 b and the first object 50 a can becalculated when the triangulation method is performed using thecombination of the first direct waves 26 a and the first indirect waves27 a and the combination of the second direct waves 28 a and the secondindirect waves 29 a, respectively. On the other hand, when thetriangulation method is performed using the combination of the firstdirect waves 26 a and the second indirect waves 29 a and the combinationof the second direct waves 28 a and the first indirect waves 27 a,respectively, positions different from the positions of the first andsecond ghosts 51 a and 51 b are calculated.

Accordingly, if the position calculated in the case where the firstsensor 21 is used as a direct detection sensor and the second sensor 22is used as an indirect sensor is the same as the position calculated inthe case where the second sensor 22 is used as a direct detection sensorand the first sensor 21 is used as an indirect sensor, it can bedetermined that a true object is present at the calculated position.

Incidentally, in a case where the first sensor 21 is used as a directdetection sensor and the second sensor 22 is used as an indirectdetection sensor when only the second object 50 b is at a position quitedistant from the second sensor 22 as shown in FIG. 6, the probing waves25 transmitted from the first sensor 21 are reflected by the secondobject 50 b, the first sensor 21 receives the second direct waves 28,and the second sensor 22 receives the second indirect waves 29. In thiscase, it may occur that the probing waves 25 a transmitted from thesecond sensor 22 are reflected by a not shown object present at aposition closer to the second sensor 22 than the second object 50 b is,and resultant direct and indirect waves are received. In this case, asshown in FIG. 7, since the second object 50 b is detected only when thefirst sensor 21 is used as a direct detection sensor, it is erroneouslydetermined that the second object 50 b is a ghost as a result ofswitching the first and second sensors with each other. If the collisionprevention control is performed based on this erroneous determination,there is a possibility of a collision between vehicle 30 and the secondobject 50 b.

Meanwhile, there is a case where the triangulation method using a directdetection sensor and an indirect detection sensor does not hold for theposition calculation as described below. The position of the secondobject 50 b is calculated as the coordinates of the intersection pointbetween the circle centered at the first sensor 21 and having a radiusequal to the first distance L1 and the circle centered at the secondsensor 22 and having a radius equal to the third distance L3. Likewise,the position of the first object 50 b is calculated as the coordinatesof the intersection point between the circle centered at the firstsensor 21 and having a radius equal to the second distance L2 and thecircle centered at the second sensor 22 and having a radius equal to thefourth distance L4. On the other hand, if the distance between the firstobject 50 a and the second object 50 is sufficiently large, nointersection point is formed between the circle centered at the firstsensor 21 and having a radius equal to the first distance L1 and thecircle centered at the second sensor 22 and having a radius equal to thesum of the second distance L2 and the fourth distance L4 minus the firstdistance L1. That is, the triangulation method using the first directwaves 26 and the second indirect waves 29 does not hold for the positioncalculation. For the same reason, the triangulation method using thesecond direct waves 28 and the first indirect waves 27 does not hold forthe position calculation.

Therefore, this embodiment utilizes the fact that no ghost is detectedif a difference between a detected distance based on the first indirectwaves 27 reflected from the first object 50 a and a detected distancebased on the second indirect waves 29 reflected from the second object50 b is sufficiently large. Specifically, an object whose detecteddistance is larger than a predetermined threshold is excluded from beinga subject of a later-explained ghost determination operation. Forexample, as shown in FIG. 6, when the second object 50 b is quitedistant from the second sensor 22, since the triangulation method doesnot hold for the position calculation in most cases, the second object50 b can be excluded from being a subject of the ghost determinationoperation.

FIG. 8 is a flowchart showing steps of the object detection processperformed by the object detection apparatus according to the abovedescribed embodiment.

This process begins in step S101 where first probing waves aretransmitted and returning waves are received in the setting where thefirst sensor 21 is used as a direct detection sensor and the secondsensor 22 is used as an indirect detection sensor. At this time, the ECU10 serves as a first acquisition unit that acquires, as a first directwave group, the first direct waves 26 and the second direct waves 28received by the first sensor 21, and acquires, as a first indirect wavegroup, the first indirect waves 27 and the second indirect waves 29received by the second sensor 22.

After an elapse of a predetermined time, second probing waves aretransmitted and returning waves are received in the setting where thesecond sensor 22 is used as a direct detection sensor and the firstsensor 21 is used as an indirect sensor in step S102. At this time, theECU 10 serves as a second acquisition unit that acquires, as a secondindirect wave group, the first indirect waves 27 a and the secondindirect waves 29 a received by the first sensor 21, and acquires, as asecond direct wave group, the first direct waves 26 a and the seconddirect waves 28 a received by the second sensor 22.

In subsequent step S103, the difference between the detected distancebased on the first indirect waves and the detected distance based on thesecond indirect waves is calculated for each of the case where the firstsensor 21 is used as a direct detection sensor and the second sensor 22is used as an indirect detection sensor for transmitting the firstprobing waves, and the case where the second sensor 22 is used as adirect detection sensor and the first sensor 21 is used as an indirectsensor for transmitting the second probing waves. Step S103 is omittedif the second direct waves and the second indirect waves are notreceived for each of these cases.

Specifically, the difference between the detected distances which aredetected based on the reception times of the first and second indirectwaves 27 and 29 of the first indirect wave group, respectively, iscalculated. Further, the difference between the detected distances whichare detected based on the reception times of the first and secondindirect waves 27 a and 29 a of the second indirect wave group,respectively, is calculated. Step S103 may be modified to calculate thedifference between the detected distances based on the first and seconddirect waves, instead of the detected distances based on the first andsecond indirect waves.

In subsequent step S104, it is determine whether or not the calculateddifference between the detected distances is larger than a threshold.This threshold is set in accordance with the distance between the firstsensor 21 and the second sensor 22. When the difference between thedetected distances is larger than the threshold, since the triangulationmethod does not hold except the correct combination of the direct wavesand the indirect waves, no ghost's position is calculated. If thedetermination result in step S104 is affirmative, that is, if thedifference between the detected distances is larger than the threshold,the process proceeds to step S105, where the combination of one of thefirst and second direct waves and one of the first and second indirectwaves is excluded from being a subject of the ghost determinationoperation. At this time, the ECU 10 serves as a first exclusion unit anda second exclusion unit.

On the other hand, if the determination result in step S104 is negative,that is, if the difference between the detected distances is smallerthan or equal to the threshold, the process proceeds to step S106 toperform the ghost determination operation.

In step S106, the position of the detected object is calculated byperforming the triangulation method for each of the combinations of oneof the first and second direct waves and one of the first and secondindirect waves, for the case where the first sensor 21 is used as adirect detection sensor and the second sensor 22 is used as an indirectdetection sensor. At this time the ECU 10 serves as a first calculationunit. Likewise, the position of the detected object is calculated forthe case where the first sensor 21 is used as an indirect detectionsensor and the second sensor 22 is used as a direct detection sensor. Atthis time the ECU serves as a second calculation unit.

Incidentally, if there is left only one combination as a subject of theghost determination operation after performing step S105, only theposition based on this one combination is calculated in step S106.

In subsequent step S107, it is determined whether or not the differencebetween the detected lateral positions (the difference of the componentsin the vehicle width direction or Y-direction of the calculatedpositions) is smaller than a predetermined threshold for each of thecombinations. At this time, the ECU 10 serves as a determination unit.It is determined that the detected object is a real object and not aghost in step 108 if the determination result in step S107 isaffirmative for at least one of the combinations. On the other hand, itis determined that the detected object is a ghost in step S109 if thedetermination result in step S107 is negative for all of thecombinations. After completion of step S108 or S109, this objectdetection process is terminated.

In the above described embodiment, the object detection process isperformed using the adjacent pair of the first sensor 21 and the secondsensor 22. However, the object detection process may be performed usingother adjacent pairs of the sensors.

In the above described embodiment, the difference between the calculatedpositions in the vehicle width direction is compared with a threshold instep S107. However, additionally, the difference between the calculatedpositions in the vehicle running direction may be compared with athreshold in step S107.

The object detection apparatus according to the above describedembodiment has the following advantages.

A detected object is determined to be a real object if the calculatedpositions of the detected object calculated respectively based on two ormore of the combinations of the sensors are the same, each of thecombinations including an adjacent two of the sensors, one of which isused as a direct detection sensor and the other is used an indirectsensor. Accordingly, it is possible to reduce the possibility oferroneously determining a ghost to be a real object.

Here, let's assume a configuration in which a detected object isdetermined to be a ghost if this object has not been detected by atleast two or more of the combinations of the sensors. In a situationwhere a plurality of objects are present in the vicinity of a vehicle,and one of the objects is quite distant from the other objects, thisobject may be erroneously determined to be a ghost according to thisconfiguration.

According to the above described embodiment, such an object isdetermined to be a real object without performing the ghostdetermination operation, if the difference between the detecteddistances calculated based on different indirect waves exceeds thethreshold, and accordingly the triangulation method does not hold forthe position calculation. Hence, according to the above describedembodiment, it is possible to reduce the possibility of erroneouslydetermining a real object to be a ghost.

Modifications

It is a matter of course that various modifications can be made to theabove described embodiment as described below. In the above embodiment,the probing waves are ultrasonic waves. However, the probing waves maybe sound waves or radio waves.

The object detection apparatus of the above embodiment is mounted on thevehicle 30. However, it may be mounted on a moving body other than avehicle such as an aircraft, a ship, or a robot. Further, the objectdetection apparatus may be mounted on a stationary body to detectdistances between the stationary body and objects around the stationarybody. This is because multiple reflection can occur between thestationary body and the objects around the stationary body. Further, theobject detection apparatus may be worn or carried by a human to detectan approaching object.

The above explained preferred embodiments are exemplary of the inventionof the present application which is described solely by the claimsappended below. It should be understood that modifications of thepreferred embodiments may be made as would occur to one of skill in theart.

What is claimed is:
 1. An object detection apparatus for detecting at least two objects present in a vicinity thereof by transmitting first probing waves from a first position and subsequently transmitting second probing waves from a second position different from the first position, a detection area of the first probing waves and a detection area of the second probing waves being partially overlapped with each other, and by receiving reflected versions of the first and second probing waves as detection data of the at least two objects, comprising: a first acquisition unit configured to acquire, as a first direct wave group including one or more first direct waves, the reflected versions of the first probing waves received as the one or more first direct waves at the first position, and acquire, as a first indirect wave group including one or more first indirect waves, the reflected versions of the first probing waves received as the one or more first indirect waves at the second position; a second acquisition unit configured to acquire, as a second indirect wave group including one or more second indirect waves, the reflected versions of the second probing waves received as the one or more second indirect waves at the first position, and acquire, as a second direct wave group including one or more second direct waves, the reflected versions of the second probing waves received as the one or more second direct waves at the second position; a first calculation unit configured to calculate a potential position for each of the at least two objects for each combination of one of the first direct waves and one of the first indirect waves; a second calculation unit configured to calculate a potential position for each of the at least two objects for each combination of one of the second direct waves and one of the second indirect waves; and a determination unit configured to determine whether one of the at least two objects is a ghost or not depending on whether the position of the one of the at least two objects has been calculated by both the first and second calculation units or has been calculated by only one of the first and second calculation units; wherein the determination unit is configured to, in the presence of the at least two objects in a vicinity of the apparatus, determine that a first object whose position is calculated by the first calculation unit is a real object if a difference between detected distances calculated based on reception times of the first direct waves reflected by the first object and a second object, or a difference between detected distances calculated based on reception times of the first indirect waves reflected by the first object and the second object is larger than a predetermined threshold, and determine that a third object whose position is calculated by the second calculation unit is a real object if a difference between detected distances calculated based on reception times of the second direct waves reflected by the third object and a fourth object or a difference between detected distances based on reception times of the second indirect waves reflected by the third object and the fourth object is larger than a predetermined threshold.
 2. The apparatus according to claim 1, wherein the determination unit is configured to, in determining whether the one of the at least two objects is a ghost or not, for each combination of one of the calculated positions of the one of the at least two objects calculated by the first calculation unit and one of the calculated positions of the one of the at least two objects calculated by the second calculation unit, determine whether or not a difference in lateral position between the calculated positions belonging to the combination is smaller than a predetermined threshold, and if the difference in lateral position between the calculated potential positions belonging to the combination is smaller than the predetermined threshold, then determine that the one of the at least two objects is a real object. 